From f278809475f6835b56de78b28dc2cc0c7e2c20a4 Mon Sep 17 00:00:00 2001 From: Aaron Thompson Date: Thu, 20 Nov 2025 10:26:33 +0000 Subject: [PATCH] debugfs: Remove broken no-mount mode debugfs access modes were added in Linux 5.10 (Dec 2020) [1], but the no-mount mode has behaved effectively the same as the off mode since Linux 5.12 (Apr 2021) [2]. The only difference is the specific error code returned by the debugfs_create_* functions, which is -ENOENT in no-mount mode and -EPERM in off mode. Given that no-mount hasn't worked for several years with no complaints, just remove it. [1] a24c6f7bc923 ("debugfs: Add access restriction option") [2] bc6de804d36b ("debugfs: be more robust at handling improper input in debugfs_lookup()") 56348560d495 ("debugfs: do not attempt to create a new file before the filesystem is initalized") Signed-off-by: Aaron Thompson Link: https://patch.msgid.link/20251120102222.18371-3-dev@null.aaront.org Signed-off-by: Greg Kroah-Hartman --- .../admin-guide/kernel-parameters.txt | 6 +----- fs/debugfs/inode.c | 18 +++++++++++------- fs/debugfs/internal.h | 13 ------------- lib/Kconfig.debug | 9 +-------- 4 files changed, 13 insertions(+), 33 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 6c42061ca20e..847a17efe289 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1113,12 +1113,8 @@ debugfs= [KNL,EARLY] This parameter enables what is exposed to userspace and debugfs internal clients. - Format: { on, no-mount, off } + Format: { on, off } on: All functions are enabled. - no-mount: - Filesystem is not registered but kernel clients can - access APIs and a crashkernel can be used to read - its content. There is nothing to mount. off: Filesystem is not registered and clients get a -EPERM as result when trying to register files or directories within debugfs. diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c index b6e401c46b6b..0284b0256195 100644 --- a/fs/debugfs/inode.c +++ b/fs/debugfs/inode.c @@ -35,7 +35,7 @@ static struct vfsmount *debugfs_mount; static int debugfs_mount_count; static bool debugfs_registered; -static unsigned int debugfs_allow __ro_after_init = DEFAULT_DEBUGFS_ALLOW_BITS; +static bool debugfs_enabled __ro_after_init = IS_ENABLED(DEBUG_FS_ALLOW_ALL); /* * Don't allow access attributes to be changed whilst the kernel is locked down @@ -365,7 +365,7 @@ static struct dentry *debugfs_start_creating(const char *name, struct dentry *dentry; int error; - if (!(debugfs_allow & DEBUGFS_ALLOW_API)) + if (!debugfs_enabled) return ERR_PTR(-EPERM); if (!debugfs_initialized()) @@ -885,21 +885,25 @@ static int __init debugfs_kernel(char *str) { if (str) { if (!strcmp(str, "on")) - debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT; - else if (!strcmp(str, "no-mount")) - debugfs_allow = DEBUGFS_ALLOW_API; + debugfs_enabled = true; else if (!strcmp(str, "off")) - debugfs_allow = 0; + debugfs_enabled = false; + else if (!strcmp(str, "no-mount")) { + pr_notice("debugfs=no-mount is a deprecated alias " + "for debugfs=off\n"); + debugfs_enabled = false; + } } return 0; } early_param("debugfs", debugfs_kernel); + static int __init debugfs_init(void) { int retval; - if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT)) + if (!debugfs_enabled) return -EPERM; retval = sysfs_create_mount_point(kernel_kobj, "debug"); diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h index 427987f81571..c95699b27a56 100644 --- a/fs/debugfs/internal.h +++ b/fs/debugfs/internal.h @@ -55,17 +55,4 @@ enum { HAS_IOCTL = 16 }; -#define DEBUGFS_ALLOW_API BIT(0) -#define DEBUGFS_ALLOW_MOUNT BIT(1) - -#ifdef CONFIG_DEBUG_FS_ALLOW_ALL -#define DEFAULT_DEBUGFS_ALLOW_BITS (DEBUGFS_ALLOW_MOUNT | DEBUGFS_ALLOW_API) -#endif -#ifdef CONFIG_DEBUG_FS_DISALLOW_MOUNT -#define DEFAULT_DEBUGFS_ALLOW_BITS (DEBUGFS_ALLOW_API) -#endif -#ifdef CONFIG_DEBUG_FS_ALLOW_NONE -#define DEFAULT_DEBUGFS_ALLOW_BITS (0) -#endif - #endif /* _DEBUGFS_INTERNAL_H_ */ diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 3034e294d50d..d9ab42916143 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -679,7 +679,7 @@ choice help This selects the default access restrictions for debugfs. It can be overridden with kernel command line option - debugfs=[on,no-mount,off]. The restrictions apply for API access + debugfs=[on,off]. The restrictions apply for API access and filesystem registration. config DEBUG_FS_ALLOW_ALL @@ -688,13 +688,6 @@ config DEBUG_FS_ALLOW_ALL No restrictions apply. Both API and filesystem registration is on. This is the normal default operation. -config DEBUG_FS_DISALLOW_MOUNT - bool "Do not register debugfs as filesystem" - help - The API is open but filesystem is not loaded. Clients can still do - their work and read with debug tools that do not need - debugfs filesystem. - config DEBUG_FS_ALLOW_NONE bool "No access" help